1. Field of the Invention
The present invention relates to a process for preparing a dental prosthesis such as an inlay, a crown, and a bridge utilizing a CAD/CAM (computer-aided design and manufacturing) apparatus. In particular, the present invention relates to a process for preparing a dental prosthesis comprising carrying out the design of a dental prosthesis at a design center where dental technicians having an expert knowledge for a CAD design are employed, by sending and receiving of a data utilizing communication means.
2. Description of the Conventional Art
Hitherto, for the preparation of dental prostheses such as inlays, crowns, and bridges, there has been generally employed a process in which a metal material or a ceramics material is cast by the lost wax casting process. Further, dental prostheses, in which the principal object is placed at aesthetics, such as ceramic inlays and all-ceramic crowns, are prepared by building up a porcelain on a refractory casting material and firing it in a vacuum electric furnace.
Usually, the preparation of dental prostheses by the lost wax casting process is carried out in the following procedures. That is, a prosthesis shape to be restored is prepared using a wax on a plaster model prepared by pouring a gypsum into an impression obtained by impression taking within an oral cavity, followed by setting; the obtained wax pattern is invested in a refractory investment; after setting the investment, the assembly is placed in an electric furnace and heated to burn the wax pattern; a metal or a ceramics material is cast in the obtained casting mold; and after cooling, the cast material is excavated from the investment, cut and polished to prepare a desired dental prosthesis such as an inlay and a crown. Further, in the case of ceramic inlays, all-ceramic crowns and the like, they are prepared in a process in which a duplicated cast is prepared using a refractory casting material; a porcelain is built up on the duplicated cast to form a desired dental prosthesis shape; and after firing in a vacuum firing furnace, the refractory casting material is removed, followed by forming the surface characterization and polishing.
Since the state of a dental caries and the intra-oral shape vary in patients one by another, a dental prosthesis to be prepared is also different in the patients one by another. Accordingly, the form of the dental prosthesis is designed and prepared based on intuition and experiences of a dental technician while taking into account the relation with antagonists or adjacent teeth or the occlusal relation. Moreover, as described above, the operation for preparing the dental prosthesis is complicated and includes many steps of manual works. Nonetheless, the completed prosthesis is required to have an extremely high dimensional precision in the order of several xcexcm. Thus, required are not only a skill of the dental technician, but also a long period of time and labors.
Under these circumstances, as a method for supplying dental prostheses having a constant quality within a short period of time stably and in a large quantity, in recent years, a CAD/CAM (computer-aided design and manufacturing) system in which a dental prosthesis such as an inlay, a crown, and a bridge is designed on a screen utilizing a computer and prepared by milling processing is paid attention. Particularly, a design and preparation system of a dental prosthesis using a CAD/CAM system represented by the Cerec system (a system of Siemens AG, Germany) has been paid attention. This CAD/CAM system is a process in which the shape of a tooth subjected to preparation of abutment tooth or cavity preparation and if necessary, the shapes of adjacent teeth or antagonists are read out; a desired dental prosthesis is designed based on the thus read out tooth shape using a computer; and a block-like material such as a resin cured material, a ceramic sintered material, and a metal material is set in an automatic milling processor and subjected to milling processing to prepare the desired dental prosthesis.
In comparison with the casting process as described above, this CAD/CAM system is characterized in that dental prostheses can be prepared with good efficiency; if the design is properly carried out, the completed dental prostheses are high in the precision; and that dental prostheses having superior fitness precision in an oral cavity can be prepared. According to the CAD/CAM system, it is possible to undergo the computation for determining the ultimate shape of the dental prosthesis (converting the shape into information for processing) through automatic computation by a computer. However, since the state of a dental caries and the intra-oral shape vary in patients one by another, it is necessary to carry out ultimately the design for ideally forming a shape of a dental prosthesis as its basis in a manual manner. In order to design and determine the shape of this dental prosthesis, required are not only a knowledge and technique of a skilled dental technician based on an anatomical shape of the tooth, but also a knowledge and technique for a design operation of highly advanced CAD. It is difficult to prepare an ideal dental prosthesis having a superior fitness precision because of difficulty of the design operation. This matter is one of the causes to inhibit the diffusion of the CAD/CAM system.
In addition, a major part of the current dental prostheses are prepared by the lost wax casting process. Accordingly, with respect to the preparation process of dental prostheses by the lost wax casting process, thorough educations are given in schools for dental technicians and the like. On the other hand, it is the present situation that educations regarding the preparation process of dental prostheses using a CAD/CAM system are scarcely given. For this reason, even when a dental laboratory employs a CAD/CAM apparatus, it is very difficult for a dental technician who, it is hard to say, has a sufficient knowledge and technique for CAD, to design an ideal dental prosthesis. Further, it is the present situation that the dimensional precision and fitness precision of the completed dental prosthesis are not so good as expected and that the preparation efficiency is not so superior as expected. Moreover, according to the CAD/CAM system that has hitherto been employed, it is required to set up all implements for the measurement, design and processing in one place, and the implements are expensive. Accordingly, it is the present situation that it is hard to say that the preparation process of a dental prosthesis utilizing the CAD/CAM system is diffused into general dental laboratories, except for large dental laboratories or dental offices.
Then, the present invention is aimed to overcome the difficulty in designing a dental prosthesis, which is the most fatal problem of the conventional art process for preparing a dental prosthesis by the CAD/CAM system as described above, and provide a process for preparing a dental prosthesis, enabling to supply dental prostheses having a constant quality within a short period of time stably and in a large quantity, the dental prostheses thus prepared being good in the precision and superior in the intra-oral fitness, an aspect of which is the original purpose of the CAD/CAM system.
In order to achieve the above-described aim, we, the present inventors, made extensive and intensive investigations. As a result, it has been found that a data obtained by measuring an intra-oral shape at a measuring center of a dental laboratory, a dental office, etc. is sent to a design center utilizing communication means; the design center where an expert having a skilled knowledge and technique for dental techniques as well as having a sufficient knowledge and technique for a CAD design is employed, is in charge of a design stage of a dental prosthesis, which is the most difficult in the CAD/CAM system, thereby carrying out concentrically the design of an ideal dental prosthesis; the design data taken by the expert is then sent to a processing center utilizing communication means and inputted into a CAM apparatus; and milling processing is carried out, whereby the resulting dental prosthesis is fitted within an oral cavity of a patient quite well, and thus, the preparation of a dental prosthesis utilizing a CAD/CAM system can be carried out efficiently, leading to accomplishment of the present invention.
Specifically, the process for preparing a dental prosthesis according to the present invention is a process for preparing a dental prosthesis utilizing a CAD/CAM system, which is characterized in that a measuring center stores three-dimensional coordinate information of an intra-oral shape measured on a basis of a plaster model prepared by impression taking within an oral cavity of a patient, or an intra-oral shape measured on a basis of an image taken by photographing within an oral cavity of a patient, as a digital signal and sends the obtained measure data to a design center using communication means; the design center reproduces the intra-oral shape on a graphic display device based on the received measure data by means of a three-dimensional graphic, designs a shape of a dental prosthesis and stores it as a digital signal, and then sends the obtained design data of the dental prosthesis to a processing center using communication means; and the processing center transmits the received design data to a milling processor as a processing command and subjects a block material to milling processing to prepare a dental prosthesis.